Maintenance policies for a production system with constrained production rate and buffer capacity

This paper considers the maintenance policies for a production system constrained by its production rate and buffer capacity to cope with unexpected failures and to deal with the variability of demand and production lead times. Using a system dynamics model, we characterize, simulate and compare results obtained by applying several maintenance policies--corrective, age-based maintenance, age and buffer-based maintenance, and modified age and buffer-based maintenance--to the system. This comparison is performed assuming that optimal values of the model parameters involved in the design of each maintenance policy have already been found by using the modified Powell method. We compare and discuss the benefits of different optimization criteria in the maintenance decision making process for a production system with constrained production rate and buffer capacity.     

Terahertz Photometer to Observe Solar Flares in Continuum

Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/s, smoothed for intervals larger than 4 s. For a 76 mm aperture, this corresponds to small solar burst intensities at THz frequencies. A system with 3 and 7 THz photometers is being built for solar flare observations on board of stratospheric balloon missions.     

Sulfonated PEEK-based polymers in PEMFC and DMFC applications: A review

Nowadays, polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are devices known for using proton conducting membranes. From a conceptual point of view, DMFC and PEMFC systems are very similar, except for being supplied by different fuels such as methanol and hydrogen, respectively. Commonly, PEMFCs are performed at temperature lower than 100 °C owing to the failure of the electrochemical performances of Nafion. Nevertheless, taking into account the poisoning effect of CO on the fuel cell catalyst (conventionally based on Pt), the ideal working temperature of the PEMFCs should be above 100 °C, where CO poisoning could be drastically reduced or avoided. Today, Nafion is recognized as the most used proton exchange membrane in the market, useful for both PEMFC and DMFC applications. It is based on a perfluorinated polymer and shows good thermal stability and high proton conductivity as main benefits. On the contrary, Nafion is an expensive material and suffers high fuel crossover (particularly, methanol crossover in DMFC applications) besides the proton conductivity loss above 100 °C. Therefore, in the last decades many scientists paid special attention on the development of new materials based on non-fluorinated polymers as an alternative to Nafion. One of the most promising class of is represented by the polyetheretherketone (PEEK). According to the specialized literature, interesting performances in terms of proton conductivity and thermo-chemical properties as well as low fuel crossover and costs are noticeable for sulfonated PEEK-based polymers. Indeed, many scientific applications are devoted to modify PEEK polymer for manufacturing membranes alternative to Nafion for both PEMFC and DMFC applications. Among them, important methods are exploited for preparing electrolyte membranes from PEEK such as: a) PEEK electrophilic sulfonation (S-PEEK); b) S-PEEK and non-functional polymers blending; c) S-PEEK, heteropolycompounds and poly-ether-imide doping with inorganic acids, etc.     

Biosynthesis of highly pure poly-γ-glutamic acid for biomedical applications

The remarkable properties of poly-aminoacids, mainly their biocompatibility and biodegradability, have prompted an increasing interest in these polymers for biomedical applications. Poly-γ-glutamic acid (γ-PGA) is one of the most interesting poly-aminoacids with potential applications as a biomaterial. Here we describe the production and characterization of γ-PGA by Bacillus subtilis natto. The γ-PGA was produced with low molecular weight (10-50?kDa), high purity grade (>99?%) and a D: -/L: -glutamate ratio of 50-60/50-40?%. To evaluate the feasibility of using this γ-PGA as a biomaterial, chitosan (Ch)/γ-PGA nanoparticles were prepared by the coacervation method at pH ranging from 3.0 to 5.0, with dimensions in the interval 214-221?nm with a poly-dispersion index of ca. 0.2. The high purity of γ-PGA produced by this method, which is firstly described here, renders this biopolymer suitable for biomedical applications. Moreover, the Ch/γ-PGA nanocomplexes developed in this investigation can be combined with biologically active substances for their delivery in the organism. The fact that the assembly between Ch and γ-PGA relies on electrostatic interactions enables addition of other molecules that can be released into the medium through changes from acidic to physiological pH, without loss in biological activity.     

Methanol steam reforming reaction in a Pd–Ag membrane reactor for CO-free hydrogen production

A dense tubular Pd–Ag membrane reactor was used to carry out the methanol steam reforming reaction for producing a CO-free hydrogen stream. A Cu/Zn/Mg-based catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 300 °C and at a H₂O/methanol feed molar ratio of 3/1. The effects of the different flow configurations, as well as the sweep factor and the reaction pressure were analysed. Experimental results in terms of CO-free hydrogen recovery, hydrogen yield, CO-free hydrogen yield and hydrogen selectivity are presented. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is proposed and discussed.     

Fabrication of hierarchical wrinkled morphologies through sequential UVO treatments

The fabrication, in a controlled manner, of well‐defined micrometer size topographical features on polymer surfaces is a great challenge due to the large variety of potential applications of these materials ranging from adhesion, optics to responsive interfaces. A challenging issue concerns the fabrication of interfaces having surface moieties with sizes at different length scales. Herein we describe the fabrication of hierarchical wrinkled surfaces involving two sequential ultraviolet‐ozone (UVO) treatments. This methodology allowed us to tailor the shape of PDMS surfaces and create a large variety of different patterns expected to have a broad range of applications requiring surface features with variable sizes. More interestingly, the employment of UVO treatments to produce surfaces with up to three distinct levels of order since they enable the rigidification of the interface by formation of a SiO_x layer or the degradation of the PDMS surface when longer treatments. The surfaces prepared by using this approach presented patterns three different scales: the structure provided by the mask employed, the wrinkled surface inside of the directly exposed areas (related to the hole size of the mask) and the wrinkled surface protected during the first treatment by the mask (which is related to the mesh dimensions of the mask employed). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41863.     

Heating and cooling energy recovery for an HVAC system: Economic analysis for the Italian climate

In this paper the economic analysis of the energy recovery in all‐outdoor‐air HVAC systems for the Italian climate is performed. The energy recovery device considered here is the same for both heating and cooling periods. During the summer season, the energy saving is achieved by evaporative cooling. The performances of the hybrid innovative HVAC system and the traditional system are calculated hour by hour by following the test reference year (TRY) profile. Such analysis is carried out taking into account simultaneously, the trend of some climatic indexes computed in order to (i) better understand the influence of climate on the HVAC system behaviour, (ii) obtain a swift feasibility analysis of the energy recovery system and (iii) perform a rough operating cost estimate of the traditional HVAC system. Copyright © 2001 John Wiley & Sons, Ltd.     

Taximeter verification using imprecise data from GPS

Until recently, local governments in Spain were using machines with rolling cylinders for testing and verification of taximeters. However, the tyres condition can lead to errors in the process and the mechanical construction of the test equipment is not compatible with certain vehicles. Thus, a new measurement device should be designed.In our opinion, the verification of a taximeter will not be reliable unless measurements taken on an actual taxi run are used. Global positioning system (GPS) sensors are intuitively well suited for this process, because they provide the position and the speed with independence from those car devices that are under test. Nevertheless, since GPS measurements are inherently imprecise, GPS-based sensors are difficult to homologate. In this paper we will show how these legal problems can be solved. We propose a method for computing an upper bound of the length of the trajectory, taking into account the vagueness of the GPS data. The uncertainty in the GPS data will be modelled by fuzzy techniques. The upper bound will be computed using a multiobjective evolutionary algorithm. The accuracy of the measurements will be improved further by combining it with restrictions based on the dynamic behavior of the vehicles.     

Filter models for conjunctive-disjunctive λ-calculi

The distinction between the conjunctive nature of non-determinism as opposed to the disjunctive character of parallelism constitutes the motivation and the starting point of the present work. λ-calculus is extended with both a non-deterministic choice and a parallel operator; a notion of reduction is introduced, extending β-reduction of the classical calculus. We study type assignment systems for this calculus, together with a denotational semantics which is initially defined constructing a set semimodel via simple types. We enrich the type system with intersection and union types, dually reflecting the disjunctive and conjunctive behaviour of the operators, and we build a filter model. The theory of this model is compared both with a Morris-style operational semantics and with a semantics based on a notion of capabilities.